It converts dozens of unit types, ranging from measurements you might use in math class -- angles and area; to science class -- temperature and force; to design class -- typography and computer file sizes.

It's also been a big hit. The app's developer Tap Tap Tap tells us that it's sold 100,000 copies of Convert since it went on sale in mid-August. After Apple's 30% cut, that's about $70,000 in sales so far, in less than a month. Not bad!

Other interesting apps for students include several digital organizers, which could replace a paper calendar and assignment notebook.

The free app MyHomework is one popular example, and it's currently the no. 2 most downloaded education app in the App Store. It lets students keep track of their classes, homework assignments, projects, and tests, with a fun, simple user interface.

College students may be more interested in iStudiez Pro, which seems more tailored to the nature of university studies, helping you keep track of lecture and lab sessions, tasks, homework, scheduling, etc. At $2.99, it's currently the no. 1 most popular paid education app in the App Store.

One apparent disappointment: An iPhone app that hooks into the Blackboard software that many schools and colleges use, which seems like it could be a great help. But we stop short of recommending the free "Blackboard Learn" app that's in the App Store.

Why? Reviewers have given it terrible grades -- a 1.5 star rating out of 5 possible stars, complaining about all sorts of shortcomings and bugs. We don't have access to a Blackboard server, so we couldn't try it first-hand. But it sounds like it could use an update.

Have any favorites for students? Let us know in the comments section and we'll add the best to our list.